1. Field of the Invention
This invention relates to a package for accommodating communication devices, such as semiconductor devices, crystal oscillators, surface acoustic wave devices, magnetic devices and capacitors, and also to a process for manufacturing the same.
2. Description of the Related Art
Ceramics have usually been used for a base member for a package for communication devices, such as semiconductor devices, crystal oscillators and surface acoustic wave devices. FIG. 6 is a sectional view illustrating a known package for a communication device. It has a ceramic base member 61 having a concavity 61a open at its top for accommodating a communication device, a ceramic frame member 62b laid on the top end surface of the ceramic base member 61, a metal frame member 62a brazed to the ceramic frame member 62b and a cover member 63 welded to the metal frame member 62a. The communication device 67 is secured on a terminal 65a and is electrically connected to a terminal 65b by a wire 64. A high-melting metal, such as tungsten W or molybdenum Mo, is used as the conductive material for the terminals 65a and 65b. The ceramic frame member 62b is metallized by nickel Ni or gold Au to allow the brazing of the metal frame member 62a thereto. A metal of low thermal expansibility is used for the metal frame member 62a to make it match the ceramic base member 61 in thermal expansibility. Kovar, a metallic material of low thermal expansibility, is usually used for the cover member 63 welded to the metal frame member 62a, since the use of a metallic material of high thermal expansibility causes inconveniences, such as the cracking of the ceramic base member 61. The package for a communication device as described requires layered sintering at a temperature close to 2000° C. between the ceramic base and frame members 61 and 62b and brazing at a temperature close to 1000° C. between the metal and ceramic frame members 62a and 62b. The joining of the members at such high temperatures and the welding of the cover member 63 to the metal frame member 62a have made it possible to achieve a gastight seal.
Reference is made to Japanese Patent Office Official Gazette JP-A-11-67950 for the related art.
The known structure and manufacturing process, however, require high costs of processing and equipment, since the terminals for supplying electricity to the communication device situated on the base member require a process including ceramics molding, repeated printing of the conductive metal and firing. Expensive jigs are also required for the highly accurate printing of the conductive metal (a high-melting metal, such as W or Mo) to form the terminals on a green sheet of ceramics. The brazing of the metal frame member to the ceramics makes it desirable for the metal to have only a small difference in thermal expansibility from the ceramics. While Kovar is usually used for the cover member, it is undesirably impossible to make a small package containing any magnetic device, since Kovar is magnetic and has to be satisfactorily spaced apart from the device. The brazing of the metal frame member to the ceramic frame member requires their gold plating which involves a high cost of material. While a package for a capacitor requires the terminals and the metal frame and cover members to be of a metallic material not reacting with the electrolyte, the selection of any metallic material other than tungsten, molybdenum and Kovar for the known structure of a package for any communication device has resulted in an undesirably large difference in thermal expansibility from the ceramics and its failure to be satisfactorily gastight.
Accordingly, every package for any communication device having a ceramic base member has involved high costs of processing, equipment, jigs and materials. It has been difficult to make a small package for any magnetic device. It has been impossible to ensure a satisfactorily high level of gas tightness for any package for a capacitor.